Electric ignition transformer



June 11, 1968 ELECTRI C IGNITION TRANSFORMER Filed Aug. 4, 1966 Wvsmor; (105626, 0- RAFPAELL/ J. G. RAFFAELLI I 3,388,362

BY 2 I United States Patent 3,388,362 ELECTRIC IGNITION TRANSFORMER Joseph G. Raifaelli, Los Angeles, Calif, assignor to International Telephone and Telegraph Corporation, New York, N.Y., a corporation of Maryland Filed Aug. 4, 1966, Ser. No. 570,245 4 Claims. (Cl. 336-73) ABSTRACT OF THE DISCLOSURE A transformer core has three legs on which are mounted, respectively, a primary winding, a secondary winding, and a shorted-turn secondary winding. A spark gap is connected in series across the secondary winding. Application of AC. power to the primary wind-ing produces recurring sparking at the spark gap.

This invention relates to an improved electric ignition means for igniting gaseous fuel particularly in connection with domestic heating systems.

There are presently two distinct types of electric ignition transformers utilized for igniting gaseous fuel in domestic heating systems; namely, the current-limiting type and the peaked type. While these devices function satisfactorily, each has certain shortcomings.

The current-limiting type transformer utilizes a somewhat conventional type transformer with a magnetic shunt and air gap between the primary and secondary windings. The magnetic shunt carries very little flux at a no-loa-d condition on the secondary, but as the secondary load is increased, the secondary ampere turns force more of the flux into the shunt until at a short circuit condition of the secondary, the output voltage is 0. The spark output characteristics of a current-limiting type of transformer are good but the transformer is difficult and expensive to build because of the introduction of the magnetic shunt.

The peaked-type transformer depends upon the the non linearity or the distortion of the flux pattern and usually requires a special core to cause the peaking action and resulting high voltage. The desired non-linearity can be introduced by external circuit elements such as capacitors or inductors c-onnectedin series with the primary; and in certain applications connected in series with the secondary. The use of a series element in conjunction with a square loop core is known to provide fast rate of change and good peaking action. Although the peaking type of transformer as an individual unit is relatively inexpensive to build, the extra non-linear component needed to provide the desire-d peaking often introduces cost which is excessive, for example, if the non-linear device is a specially designed capacitor. On the other hand, certain peaking transformer assemblies employ relatively inexpensive capacitors in the secondary circuit, but great difficulty and cost is encountered in efiiciently building such transformer and particularly in providing high voltage insulation.

It is a primary object of this invention to provide an improved ignition transformer which provides adequate output but is compact and inexpensive to manufacture.

It is a further object of this invention to provide such a transformer which requires neither magnetic shunts nor costly external circuit elements to attain the non-linearities necessary to peak the voltage.

The peaking type ignition transformer of the present invention includes a three legged core made of magnetic material having nearly :a square hysteresis loop characteristic. A primary winding is wound on one leg and con- 3,388,362 Patented June 11, 1968 ICC nected to a source of power; a secondary winding having more turns than the primary coil is wound on the middle or second leg, and a closed or shorted turn is mounted on the third leg of the core. The shorted turn may consist of an encircling strip of aluminum or copper. The secondary winding is terminated with its start or inside winding connected to the core terminal and its finish or outside winding connected to a high tension standoff terminal.

As the flux is built up within the core, by the energization'of the primary coil, the spark gap between the ignition terminals breaks down causing current to be momentarily carried in the secondary coil. Thereafter, the spark ceases. This action induces current in the shorted turn which causes a rapid rate of change of flux that is reflected back to the secondary, which is no longer conducting; this again inducing a higher voltage and causing the spark gap to again break down and again induce current in the shorted turn. In other words, an oscillatory action is set up between the secondary and the shorted turn and each time a spark occurs at the gap, a pulse of current is generated and flux is induced in the shorted turn, thus setting up a flywheel type action.

For a more detailed description of the invention reference may be had to the following description and drawing in which:

FIG. 1 is a plan diagrammatic view of the transformer of the invention; and

FIG. 2 is a circuit diagram of the transformer of FIG. 1.

Referring now to FIG. 1, the transformer of the invention may be seen to include a core 10 having three parallel legs: an outer leg 12, an inner leg 14, and another outer leg 16 connected by end members on yokes 18 and 19. As can be seen, the middle leg 14 has a cross section considerably larger than leg 16.

A primary coil winding 20 is wound around leg 12 and has connected thereto a pair of leads 22 and 24 to be connected to a source of alternating current. A secondary winding 26 is wound around middle leg 14 and one end of the winding is connected to a ground as indicated by terminal 28 while the other end of the winding is connected to a terminal 30. The number of turns of the secondary winding 26 is larger than the number of turns on the primary winding 20.

In accordance with the invention, a third winding 32 comprising a shorted turn made of a piece of aluminum or copper tube or a seam welded strip, is mounted on core leg 16. The core is made of magnetic material that is grain oriented and has nearly a square hysteresis loop characteristic.

The transformer of FIG. 1 is illustrated schematically in FIG. 2 which is perhaps most convenient for discussing the operation of the construction. Voltage is applied to the primary 20 of the transformer through a series limiting resistor 34. The turns ratio of the transformer is high; and since the primary is driven rapidly to saturation, a non-linear flux pattern is achieved which has a tendency to peak the voltage induced in the secondary winding 26. The core has the ability to follow very rapid changes, thus allowing maximum use to be made of the non-linearity of flux. Since middle leg 14 of the core is considerably larger than leg 16, practically all of the flux appears in the middle leg on which the secondary winding is wound until the secondary voltage is large enough to break down the spark gap between terminals 28 and 3t); and at this time current flows momentarily in the secondary circuit and generates one spark-over.

As current flows through the secondary circuit, it causes a change of flux in the core leg 14 which induces a rapid rate of change of flux in core leg 16 thus inducing a relatively large pulse of short circuit current in the winding or turn 32. This current again causes a rapid change of flux in the core which is reflected back to the secondary Winding 26 which is no longer conducting. The voltage thus induced on the secondary winding 26 causes the gap between terminals 28 and 30 to again break down. In other words, once the spark gap breaks down, an oscillatory action is established between the secondary and the leg 16 carrying the shorted Winding 32; and each time a spark appears at the gap, a pulse of current is conducted and flux is induced in the leg with the shorted turn. Thus, in effect, a flywheel type action is established. In the meantime the primary winding 20 is supplying the losses incurred in the circuit.

As mentioned, the bulk of the flux introduced to the core by primary winding 20 passes through middle leg 14 'but a certain amount naturally also passes through outer leg 16. Consequently, some peaking of the secondary voltage is attained due to the fact that this small amount of leakage flux appears in the leg 16 even before the spark gap breaks down. This tends to give about a increase in the peak output voltage.

The main advantage of the transformer of the invention is that in addition to providing a high output voltage, it can be fabricated .in a compact package and is much cheaper to manufacture than other transformers providing comparable operation. The arrangement of the invention requires neither magnetic shunts, adding to the bulkiness of a device, nor costly external circuit elements to attain the non-linearities to peak the voltage. The coils of the transformer are random Wound on bobbins which is a very inexpensive coil construction that can be utilized in large production quantities. The insulation problem in the secondary may be overcome by vacuum impregnating with a silicone encapsulant or a high voltage epoxy or by immersing in a dielectric type oil. Such construction may be easily fabricated in a compact package.

While only a single embodiment of the invention has been illustrated and described, it should be understood that various modifications and changes may readily come to the mind of one skilled in the art. Accordingly, it is intended that all such changes and modifications that fall within the true spirit and scope of the invention be included in the appended claims.

What is claimed is:

1. A peaking-type transformer for generating a fueligniting spark comprising:

an electrically conductive core including three interconnected legs made of material having a square hysteresis loop characteristic;

a primary winding supported on a first leg of said core and adapted to be connected to a source of AC. power;

a second, winding supported on a second leg of said core and having more turns than said primary winding;

a pair of spaced terminals constituting a spark gap connected in series in said second winding with one of said terminals forming a low voltage terminal while the other terminal forms a high voltage terminal;

and a short circuited third Winding mounted on the third leg of said core and cooperating with the second winding upon striking of a spark across the spark gap to initiate oscillatory magnetization of the core to produce recurrent sparks in the spark gap.

2. The transformer of claim 1, in which the three legs of the core extend in generally parallel relation and are connected at their ends by yokes perpendicular to the legs, and the third winding is supported on the third leg.

3. The transformer of claim 1, in which the low voltage terminal of the second Winding is grounded to the core.

4. The transformer of claim 1, wherein said third winding is a single shorted turn having a relatively large crosssection.

References Cited UNITED STATES PATENTS 1,719,445 7/1929 Oiney 33673 1,722,444 7/1929 Reiche 33673 1,812,949 7/1931 Halpet'in et a1. 33673 1,910,381 5/1933 Dowling 323 XR 2,118,137 5/1938 Bartlett 33673 XR 2,406,045 8/ 1946 Stevens 33673 3,215,961 11/1965 Dortort 33673 XR DARRELL L. CLAY, Primary Examiner.

T. J. KOZMG, Assistant Examiner. 

